Process and device for regulating the calorific output in a continuous annealing and processing line for continuously cast metal products

ABSTRACT

A process and device are disclosed for regulating the annealing power in at least one annealing section of a continuous annealing and processing line for continuously cast metal products. The speed of the cast products (D) passing through the continuous annealing device is detected, as well as the voltage currently applied to the annealing section, which is converted into an effective value (U c ) by means of a control device (50). The voltage supplied to the annealing section is modified by a control signal derived from the determined effective value of the voltage, in order to achieve a predetermined annealing power value dependent on the measured speed. At least the current flowing in one annealing section is also detected and converted into an effective value. The annealing power actually supplied to the annealing section is calculated from said effective values. The voltage value is modified by a control device until a predetermined value of the annealing power is reached.

BACKGROUND OF THE INVENTION

The present invention relates to a process and a device regulating thecalorific output in a resistance annealing plant.

Description of Related Art

A continuous resistance annealing and processing line is used forsubjecting continuously cast metal products to heat treatment, the term"continuously cast metal products" here denoting wire made of ferrousand nonferrous metals, in particular copper, but also bundles ofparallel, twisted or stranded wires made of these materials. To simplifymatters, the term "wire" is used for characterizing these products inthis document.

In a continous annealing and processing line the wire is led over atleast two contact elements having a different voltage potential, suchthat a current runs through the wire resulting in its heating.Preferably rotating rollers are used as contact elements, having acircumferential speed principally equal to the passing speed of thewire; however, electrolytes and molten metal baths as well as fixedcontact elements may be used. The problems of regulating the calorificpower in such a continous annealing and processing plant and thesolution as provided for by this invention are detailed in the exampleof a three-phase current annealing plant for thin copper wires. However,using this example shall in no way be understood as a limitation of theapplicability of the present invention to resistance annealing plants ingeneral, rather may the invention also be used for other continousannealing and processing plants, such as DC annealing plants.

As is generally known, flexible electric lines normally have copperstrands, manufactured of individual wires having a diameter of e.g. 0.2mm. In case one or several of these individual wires of the strand breakduring use, not only the electric conductivity is impaired, but inparticular the danger arises that individual wires penetrate theelectric insulation, resulting in a considerable danger of accidents.

Therefore the mechanical quality of such strands, in particular thefatigue strength under reversed bending stresses has to meet highrequirements which have been laid down by VDE (Association of GermanElectrical Engineers) in the Federal Republic of Germany.

If the copper wire used for manufacturing brands is drawn to its finaldiameter in a wire drawing machine, the metal structure changes and thewire becomes hard and brittle and has only a low fatigue strength underreversed bending stresses. In order to give the wire the desiredmechanical properties, it is subsequently subjected to a heat treatmentin a continous annealing and processing plant. To guarantee the desiredquality, the achieved annealing temperature of the wire has to be withina strictly defined temperature range, and if the temperature falls belowthis range or exceeds it, this results in a quality impairment and--as aconsequence--in refuse.

In order to assure that the desired temperature range is reached, itwould be advantageous, if the temperature of the passing wire could bemeasured exactly. However, this meets with difficulties as--on the onehand--the wire runs through the wire annealing plant at high speed (e.g.10-30 m/s) and--on the other hand--the wire surface is very small due tothe small diameter, such that here the prior art methods for measuringthe surface temperature will not be successful.

As described in DE 40 10 309 C1 the regulation of such continousannealing and processing plants is therefore performed via regulatingthe calorific power according to the equation

    U.sub.e =G·√v,                             (F1)

U_(e) being the effective value of the heating voltage, v being thespeed at which the wire passes through the continous annealing andprocessing plant and G being the so-called annealing factor, a product-and plant-specific value. Normally the output regulation is performed bymeans of thyristors in antiparallel connection, whose firing angle iscontrolled adequately.

Although this prior art regulation process and this prior art regulationdevice works satisfactorily in many applications it turned out that afurther quality increase in the ultimate product is not possible, inparticular when annealing thin wires. In order to reach such a qualityincrease it is necessary to heat the wire in the annealing plant inaccordance with an accurately predetermined temperature profile, i.e. inparticular the deviations of the achieved maximum temperature from thedesired rated value shall only be small. For achieving a constantquality level it is also important that this temperature profile will bereached during the overall operating period of the relevant contactelements, i.e. the contact rollers.

Therefore the present invention is based upon the task to creat animproved procedure and an improved device for regulating the calorificoutput in a continous annealing and processing plant for continouslycast metal products, achieving an exactly reproduceable temperaturemarch, mostly independent of outside influences such as wear of contactrollers or brushes.

As provided for by this invention this task is solved by a processdisclosed herein.

The device as provided for by this invention is also disclosed herein.

The process as provided for by this invention offers the possibility tomeasure the annealing power supplied to the wire very exactly andindependently of possible surface wear on the contact elements orrollers. As is state of the art, the process as provided for by thisinvention measures the wire speed, thus giving the amount of wirepassing through the annealing plant per time unit. An accordinglyprogrammed control device calculates from the wire speed which annealingoutput has to be supplied to the wire for reaching the desired wiretemperature. In case the annealing plant includes several individualannealing sections, there might be a separate allowance of the annealingoutput for each individual annealing section. Then the annealing outputserves to derive a rated value for setting the effective value of theannealing voltage by means of the phase control. Consequently a plannedstatus is given which may, however, differ considerably from the actualstate, e.g. in dependence on the transition resistances between thebrushes and the rotating contact rollers, on the transition resistancesbetween the contact rollers or the contact elements and the wire and soon.

In order to minimize these deviations, the annealing voltage supplied tothe contact elements will be measured and digitized in an analog todigital converter. In addition the current in the wire will be measured.This value will also be digitized. The digitized values of current andvoltage will serve to calculate the effective values and the overallannealing output supplied to the wire and compared with the actualvalue. In case of deviations of the actual value, the voltage regulationwill be changed accordingly.

The process as provided for by this invention includes considerableadvantages as compared to prior art processes. In conventional processesthe effective value of the annealing voltage is created by squaring thevoltage signal in an electronic component. However, this value includesan error having more or less decisive effects, as the effective valuecomposer forms an exactly correct value only for a certain curve, e.g.only for a sinusoidal course. By digitizing the values and calculatingthe effective value from the digitized values, the control accuracy willbe considerably improved.

In addition the measurement of the current in the passing wire permits afurther accuracy increase of the annealing power regulation. The overallvoltage on the contact elements is only the voltage on the individualwire section, if there are no transition resistances between the voltagesupply line to the contact element and the wire itself. For example, atransition resistance between a brush and a rotating contact rollerand/or between the contact roller and the wire due to wear orcontamination, results in an overall resistance increase and thus in adecrease of the current flowing through the wire. In a conventionalplant the transition resistances consequently reduce the temperatureachieved, without having the possibility to grasp it by means of theregulation.

Measuring the voltage and the current flowing through the wire alsopermit the detection of wear on the contact elements. If the currentflowing through the wire decreases during operation although the sameeffective voltage is applied, this normally indicates an increase intransition resistances and this usually means wear. The optimum time forreplacing or reworking the contact elements may thus be determined bychecking the transition resistances.

The arrangement for regulating the annealing output as provided for bythis invention includes units to detect the relevant instantaneous valueof the voltage and current on the annealing section. The voltage ismeasured in the conventional way. The current may be measured in thesupply lines, however--in particular when using an annealing plant withseveral annealing sections arranged consecutively--the use of a currentmeter capable of measuring the current flowing directly in the wire, ispreferred. As provide for in this invention a slotted iron ring is usedfor measuring this current, the wire runs through it without touching itand a Hall probe measures the magnetic flux induced by the currentflowing through the wire.

The detection of the current flowing through the wire has the advantagethat thus the influence of leak currents will be eliminated. Such leakcurrents appear e.g. in case of contact roller or electrolytecontamination.

In case an annealing plant with several annealing sections is used, i.e.a three-phase current annealing plant, the current measurement may beperformed in each annealing section. If the amount of equipment is to bereduced, it is also possible to measure the current only in the last orin the first and the last annealing section.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, features and application possibilities of thepresent invention result from the subsequent description of theembodiment examples and the relevant figures:

FIG. 1 shows a functional diagram of an embodiment example of thearrangement as provided for in this invention.

FIG. 2 shows a non-dimensional representation of the course of theannealing voltage during a test;

FIG. 3 shows the amplitude range of the curve in accordance with FIG. 2;

FIG. 4 shows the measured course of the annealing current with regard totime during a test;

FIG. 5 shows the effective current value derived from the current coursein accordance with FIG. 4;

FIG. 6 shows a diagram, giving the voltage value, the current valuemeasured during a test and the output calculated in non-dimensionalunits with regard to time;

FIG. 7 shows a perspective view of a transducer for measuring thecurrent.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiment example according to FIG. 1 shows the application of thepresent invention in a three-phase current annealing arrangement, with acopper wire having a diameter of 0.63 mm running through it. The wirespeed is ÷10 m/s.

The three-phase current annealing plant includes four contact rollers 1,2, 3, and 4, shown on one level in the diagram according to FIG. 1. WireD moves at speed v in the direction of arrow 5 through the wireannealing arrangement, the speed is measured by a tachometer generator7.

The contact rollers 1 to 4 will be supplied by a three-phase network 9,having three phases R, S, T, which are arranged out-of-phase by 120°, asis state of the art. The phases of the three-phase current are connectedto three AC power controllers 10, 11, 12, each consisting of twothyristors 15, 16 in antiparallel connection and of two resistors 17,18.

The AC power controllers 10, 11, 12 each are connected with the primaryof one of the three transformers 21, 22 and 23, which are connected in atriangle with regard to the primary. With regard to the secondary thethree transformers 21, 22, 23 form an y-delta connection. The exit oftransformer 21 leads to contact roller 1 and 4, the exit of transformer23 to contact roller 2 and the exit of transformer 21 to contact roller3. As contact roller 1 and contact roller 4 have the same voltagepotential, the annealing arrangement as a whole is electrically neutral.

The annealing voltages U₁, U₂, U₃ on the annealing sections I, II, IIIwill be measured by the measuring units 30, 31, 32 and transformed to adigital voltage value in the transformer units 35, 36, 37. Eachtransformer unit 35, 36, 37 includes an insulating amplifier, topped bya low-pass filter with a 1000 Hz cut-off. The filter's output signal isled to a analog-to-digital transformer and digitized. The scanning isperformed at intervals of 500 82 s, the resolution is 12 Bit.

The current flowing through the wire in the annealing sections I, II,III is measured by the sensors 40, 41 and the sensor still will bedetailed with respect to FIG. 7. The variable measured will be digitizedin the transformer units 45, 46, 47. Similar to the transformer units35, 36, 37 for the voltage values, the transformer units 45, 46, 47 forthe current values consist of a low-pass filter with a 1000 Hz cutofffrequency, topped by an analog-to-digital converter. Scanning rate andresolution are identical with those of the transformer units 35 to 37.

Even the output voltage of the tachometer generator will be digitized ina transformer unit 48.

The digitized values will be passed on to a processor 50, preferably amicroprocessor, where the effective values for voltage and current aregained from the digitized values and the effective annealing output inthe individual annealing sections will be determined, as will bedetailed below.

For controlling the AC power controller the processor emits 50 controlsignals; in the signal generating units 53, 54, 55 they will betransformed into control signals suitable for driving the AC powercontroller.

The sensors 40, 41 and 42 for measuring the current in the annealingsections consist of an iron ring 70, as shown in FIG. 7, interrupted bya gap 71. A Hall probe 73 with supply lines 74, 75 is glued into the gap71.

The current flowing in the annealing sections induces a magnetic flux inthe iron ring 70, measured by the Hall probe 73 in the gap 71. The Hallvoltage on the supply lines 74, 75 may be immediately converted into thecurrent flowing through the annealing section.

Using such a measurement system for measuring the current in a wireannealing arrangement has particular advantages. On the one hand acontactless measurement is performed, subjecting neither the wire northe sensing element to any kind of wear. In addition the measurementsystem is mostly insensitive to contaminations. As the Hall probevirtually works without inertia, the current may be taken very preciselyand with an exact course of time.

In principle the sensing element depicted in FIG. 7 is designed as onepiece, i.e. the wire has to be threaded through the opening in ring 70.A divisible ring may also be used instead, into which the wire only hasto be inserted.

Instead of a divided ring, the Hall probe itself may be designed in sucha way that it can be taken out, such that the wire may be laid into thering through the gap provided for the Hall probe.

The function of this arrangement is now explained with relation to FIGS.2 to 6.

FIG. 2 gives a non-dimensional representation of the course of time ofthe annealing voltage during a time period of 25 ms, the wire passingspeed being 10 m/s. As mentioned before and also valid for the otherfigures the wire diameter was 0.63 mm. This measuring result and thoseof the other figures relates to the last annealing section III.

A non-dimensional voltage parameter is entered on the ordinate 80 andthe time on the abscissa 81. The course of the annealing voltage isreferred to as 82.

As can be seen from FIG. 2, the voltage course deviates significantlyfrom a sinusoidal course. Forming an effective value based upon amathematically exact sinusoidal course therefore leads to major errorsin case of such voltage courses.

FIG. 3 reflects the amplitude range of the annealing voltage curveaccording to FIG. 2.

A non-dimensional amplitude parameter is entered on ordinate 83 and thefrequency in kHz on the abscissa 84.

The amplitude course with respect to time is referred to as 85.

FIG. 4 gives the course of time of the current 92 in the annealingsection III for a predetermined time interval. A non-dimensionalannealing current parameter is entered on ordinate 90 and the time onabscissa 91.

FIG. 5 shows (for a longer time interval than FIG. 4) the effectivevalue 97 of the current, a non-dimensional parameter of the currentagain being entered on the ordinate 95 and the time on abscissa 96. Itis interesting to see that the current is subject to major fluctuationsdespite constant wire passing speed.

On the basis of the voltage and current values measured for each of thethree annealing sections the processor 50 determines the annealingoutput in the individual annealing sections by multiplying the relevanteffective voltage and current values.

FIG. 6 shows in three diagrams, arranged one upon the other, theannealing voltage, the annealing current and the annealing output inannealing section III. In the uppermost diagram 110 a non-dimensionalvoltage parameter is entered on ordinate 111 and the time on the timeaxis 112. The curve 113 gives the non-dimensional voltage parameter.

In diagram 120 a non-dimensional current parameter is indicated onordinate 121 and the time on abscissa 122, the units are identical tothat in diagram 110. Curve 123 reflects the course of a non-dimensionalannealing current parameter with regard to time.

In the third diagram 130 a non-dimensional parameter for electric poweris entered on ordinate 130 and the time on abscissa 132 in the sameunits and at the same time as in diagrams 110 and 120. Curve 133reflects the instantaneous annealing output calculated by processor 50.

For each annealing section I, II and III the processor 50 now comparesthe instantaneously fed power with the annealing output, required forthe relevant speed. This may be done by evaluating the above formula.However, it is also possible to store an adequate performancecharacteristics for the desired annealing power values in a memory ofthe control unit 50; the relevant required annealing output for theannealing sections I, II and III will then be determined by the help ofthis memory, possibly by interpolation.

If there appears a difference between the desired annealing output andthe measured annealing outputs, the signal gnerating units 53, 54, 55will be influenced accordingly in order to change the annealing voltagein the individual annealing sections such that the deviation will beminimized. This guarantees a very rapid and precise regulation of theannealing output, having positive effects on the quality of the wiremanufactured.

Apart from this regulation task the processor has to monitor themeasured variables to detect an irregular operation of the system, inparticular wear On brushes and/or contact rollers.

As the wire resistance in the individual annealing sections is known, itmay be determined, whether a major, not desired voltage drop occurs inthe current transfer from brush to contact roller and/or from contactroller to wire. If it is detected that the voltage required forgenerating a certain annealing current is higher than a predeterminedlimit value, a signal will be emitted to show the malfunction of theannealing plant.

Instead of calculating the voltage drop comparative values may be storedin a table, stating which annealing voltage is required for correctoperation, in order to incite a certain annealing current. In case themeasured effective voltage values exceed these stored values by acertain amount, this indicates an undesirably high transitionresistance.

In addition the processor 50 monitors the time fluctuations of annealingcurrent and annealing output. If the annealing current is subject tomajor time fluctuations, this is a distinct indication for irregularcurrent transmission. This indicates wear on the contact rollers. Theeffective value of the annealing current and the annealing output withregard to amplitude fluctuation and with regard to fluctuation frequencywill be investigated for assessing the fluctuation. The values of theannealing current and annealing ouput already available in digital formwill be subjected to numerical statistical procedures for curveassessment, as is prior art.

The arrangement and the process described above permit a very exactdetection and regulation of the annealing output, thus the wire will beheated exactly according to the desired temperature profile. Contrary toprior art arrangements the deviations in annealing output may bedetected especially by transition resistances and balanced byregulation.

In the embodiment example given each annealing section I, II and III isregulated individually to the predetermined annealing output value. Tosimplify the structure it is also possible to regulate only one or onlytwo annealing sections instead of all three annealing sections. If onlyone annealing section will be regulated, annealing section III willpreferably be regulated, if two annealing sections will be regulated,annealing section I and annealing section III will preferably beregulated.

Furthermore it is possible to combine the regulation of annealingsection I and II in one regulation.

If at least two annealing sections will be regulated according to theabove described process, it is also possible to compensate for a plantstandstill and the resulting cooling down of the wire within theannealing arrangement. As described in DE 40 10 309 C1, the annealingpower fed to the last annealing section III will be increased during apredetermined period of time to such an extent that the cooling down inthe annealing plant will be compensated. At a time interval of 500 μsbetween the individual scannings and a wire speed of 10 m/s theindividual measurement points with relation to the wire have a distanceof 5 mm, thus permitting a very exact regulation.

What is claimed is:
 1. A process for regulating an annealing power in atleast one annealing section of a continuous annealing and processingline for continuously cast metal products, comprising the stepsof:measuring a passing speed of the continuously cast metal products (D)passing through the continuous annealing and processing line andoutputting a representative electrical signal by means of a firstmeasuring system (7), measuring an instantaneous voltage value on theannealing section and outputting a representative electrical signal bymeans of a second measuring system (30, 31, 32), transforming themeasured instantaneous voltage value into an effective voltage value(U_(e)), and forming a control signal on the basis of the effectivevoltage value by means of a control unit (50) for changing a voltagesupplied to the annealing section in order to obtain a predeterminedannealing power value which is dependent on the speed measured,characterized by the steps of detecting a current flowing in at leastone annealing section by means of a third measuring system (40, 41, 42),digitizing and integrating the instantaneous voltage value or values atthe annealing section in order to determine the effective voltage valuefor a respective short period of time each, digitizing and integrating ameasured instantaneous value of the annealing current in order todetermine the corresponding effective value for the same respectiveshort period of time as in the case of the annealing voltage, andproviding the control unit as a processor for multiplying the calculatedeffective values of the annealing voltage and the annealing current inorder to calculate the annealing power actually supplied to theindividual annealing section and to compare it with the predeterminedannealing power.
 2. The process according to claim 1, comprising thestep of contactlessly measuring the current flowing in said at least oneannealing section on a wire located in the annealing section.
 3. Theprocess according to claim 1, comprising the step of measuring theelectrical resistance on the basis of the measured effective values ofthe annealing voltage and of the measured effective values of theannealing current and outputting an alarm signal if this resistanceexceeds a predetermined value by means of the processor.
 4. The processaccording to claim 2, comprising the step of measuring the electricalresistance on the basis of the measured effective values of theannealing voltage and of the measured effective values of the annealingcurrent and outputting an alarm signal if this resistance exceeds apredetermined value by means of the processor.
 5. An arrangement forregulating an annealing power in at least one annealing section of acontinuous annealing and processing line for continuously cast metalproducts, comprising:a first measuring equipment (7) for measuring apassing speed of the continuously cast metal product (D) passing throughthe continuous annealing and processing line and for outputting arepresentative electrical signal, a second measuring equipment (30, 31,32) for measuring an instantaneous voltage value on the annealingsection and for outputting a representative electrical signal, a firstdetermining equipment for determining an effective voltage value (U_(e))on the basis of said measured instantaneous voltage value on theannealing section, a control unit (50) for forming a control signal fromsaid determined effective voltage value for changing the voltagesupplied to the annealing section in order to obtain a predeterminedannealing power value dependent on the speed measured, a third measuringequipment (40, 41, 42) for emitting a measuring signal representative ofannealing current flowing in said at least one annealing section, and asecond determining equipment for determining an effective current valueon the basis of said measured instantaneous current value, said firstand second determining equipment including a first (35, 36, 37) and asecond (45, 46, 47) transforming equipment having a digitizing unit fordigitizing the measured instantaneous values of voltage and current, andeach transforming equipment is followed by an integrating equipment fordetermining the corresponding effective value from this digitized valuefor a predetermined short period of time, and the control unit isdesigned as a processor and includes a multiplication equipment forcalculating the annealing power actually supplied to the respectiveannealing section from said calculated effective values.
 6. Thearrangement according to claim 5, characterized in that the thirdmeasuring equipment (40, 41, 42) is provided as a induction measuringinstrument for contactlessly detecting the current flowing through theannealing section.
 7. The arrangement according to claim 5,characterized in that the first and second equipment are designed suchthat the distance of time, in which the individual measured values aretaken and digitized, is less than 5 ms.
 8. The arrangement according toclaim 5, characterized in that the first and second equipment aredesigned such that the distance of time, in which the individualmeasured values are taken and digitized, is less than 1 ms.
 9. Thearrangement according to claim 6, characterized in that the thirdmeasuring equipment (40, 41, 42) is designed as an iron ring (70)interrupted by a gap (71) and a Hall-probe (73) is arranged in the gapfor measuring the magnetic flux in the iron ring.
 10. The arrangementaccording to claim 6, characterized in that each transforming unit (35,36, 37, 45, 46, 47) includes a low-pass filter followed by an analog todigital converter.
 11. The arrangement according to claim 6,characterized in that the first and second equipment are designed suchthat the distance of time, in which the individual measured values aretaken and digitized, is less than 5 ms.
 12. The arrangement according toclaim 6, characterized in that the first and second equipment aredesigned such that the distance of time, in which the individualmeasured values are taken and digitized, is less than 1 ms.
 13. Thearrangement according to claim 9, characterized in that the iron ring isdesigned as a divisible ring in order to facilitate inserting of a wire.14. The arrangement according to claim 9, characterized in that eachtransforming unit (35, 36, 37, 45, 46, 47) includes a low-pass filterfollowed by an analog to digital converter.
 15. The arrangementaccording to claim 9, characterized in that the first and secondequipment are designed such that the distance of time, in which theindividual measured values are taken and digitized, is less than 5 ms.16. The arrangement according to claim 9, characterized in that thefirst and second equipment are designed such that the distance of time,in which the individual measured values are taken and digitized, is lessthan 1 ms.
 17. The arrangement according to claim 13, characterized inthat each transforming unit (35, 36, 37, 45, 46, 47) includes a low-passfilter followed by an analog to digital converter.
 18. The arrangementaccording to claim 13, characterized in that each transforming unit (35,36, 37, 45, 46, 47) includes a low-pass filter followed by an analog todigital converter.
 19. The arrangement according to claim 13,characterized in that the first and second equipment are designed suchthat the distance of time, in which the individual measured values aretaken and digitized, is less than 5 ms.
 20. The arrangement according toclaim 13, characterized in that the first and second equipment aredesigned such that the distance of time, in which the individualmeasured values are taken and digitized, is less than 1 ms.
 21. Thearrangement according to claim 17, characterized in that the first andsecond equipment are designed such that the distance of time, in whichthe individual measured values are taken and digitized, is less than 5ms.
 22. The arrangement according to claim 17, characterized in that thefirst and second equipment are designed such that the distance of time,in which the individual measured values are taken and digitized, is lessthan 1 ms.